Overview

Pure-breeding is the predominant practice with yak. Apart from
a scheme involving selection in crossbreds of wild yak with domestic yak in a
process of breed development (see Chapter 2), no information has become
available on rigorous selection programmes consistently applied for the
improvement of the performance of yak in China. However, some selection schemes
appear to be under consideration both in China and other countries. The dearth
of organized selection schemes is not surprising with an absence of written
records of performance and pedigrees and because of the location of yak in harsh
environments and remote regions. Herdsmen in some areas, such as those of the
Jiulong yak, have a traditional system of selection for replacement bulls. The
Jiulong scheme considers the performances of the sires and maternal performance,
as well as the physical appearance of the individual. It has to be remembered
that the capacity to survive must be one of the chief attributes in the genetic
makeup of the yak. This characteristic is likely to be under constant pressure
from natural selection.

There is circumstantial evidence that some inbreeding is
likely to have occurred with yak as a result of traditional pure-breeding
methods and, in some countries, because of insufficient interchange of breeding
stock across national boundaries. This can be expected to have harmful effects
on the performance of yak.

Crossbreeding among the different types and breeds of yak does
not appear to be systematic, but, on theoretical grounds, should be
advantageous. Crossing domestic yak with wild yak is receiving widespread
attention and favourable results are reported, with indications of heterosis.
Crosses of domestic yak with wild yak are also thought to provide a basis for
selection in new breed formation (cf. Chapter 2).

Hybridizing of yak with other species of cattle (mainly Bos
taurus but also Bos indicus in some countries) is widely practised.
Bulls of local breeds of cattle are used for natural service. But for
hybridizing of yak with relatively high-yielding "exotic" breeds of cattle, the
use of AI with frozen semen is normal, as the bulls of these breeds have not, in
the past, survived for long in the mountainous regions. Hybridizing of yak with
cattle is advocated in several countries as a means of increasing milk and meat
output from the mountainous regions. Only the first generation of hybrids (F1)
is favoured, as later generations of backcrosses have poorer performance (and
hybrid males are sterile). However, the F1 females can usefully be mated to
males specially chosen for "meat" production. There are both economic and
biological limits on the extent to which interspecies hybridization can be
carried out. The biological limit is set by the low reproductive rate of yak and
by survival rates. A large proportion of the female yak population is required
simply to replace the pure-bred yak - even if the size of that population were
to remain static and not increase, as seems often desired by herders.

Pure-breeding

Ways of improving yak productivity by selection might be of
great importance to the people who depend on yak for their livelihood. As
discussed earlier, the yak is the dominant domestic animal in the alpine regions
and the mountain plateaux of western China and adjacent areas to the south and
north - dominant in economic, though not necessarily in numerical, terms. The
yak also has great importance in Mongolia and several other countries (see
Chapter 11, part 2). It is an integral component of the socio-economic system of
people in many remote areas and, often along with sheep and goat, it is the main
contributor to the livelihood of the herdsmen and their families. And yet,
several factors militate against systematic breeding programmes.

The first of these constraints on improvement by genetic
selection is that yak are still widely regarded, especially among Tibetan
people, as a symbol of wealth. The more yak a family or a village owns, the
richer and stronger it is considered to be. To maintain or increase the number
of yak can take precedence over improvements in quality, or even overall
productivity. Thus, animals are often kept until they die rather than culled for
reasons of poor productivity. This can lead to overstocking of pastures and to a
potential reduction in the output from the herd as a whole (see Chapters 12 and
13). "Quality" of the herd can become more of a consideration in situations
where "competing" families or villages already own similar numbers of animals.
Observation also suggests that smaller herds are sometimes of better quality
because more pasture resource is available for a given number of animals and
greater individual care is given to the animals by the herders.

A second important reason why genetic selection by herdsmen,
or by extension officers acting on their behalf, is impeded is the absence of
the necessary performance and parentage records - although herdsmen will often
claim to know the parents of yak, especially bulls. It is doubtful if the
accuracy of this knowledge is ever tested. In some nucleus breeding herds set up
recently on the state farms in Qinghai, Tibet, Gansu and Sichuan, pedigrees but
not performance were recorded.

Third, survival of the yak in a harsh, even hostile,
environment is of paramount importance, perhaps of higher priority than any
other single performance trait (though it is unlikely that this matter has been
quantified). In terms of selection for survival under these conditions, natural
selection is almost certainly more effective than any current procedure devised
by man.

In relation to selection for the main products from the yak -
milk, meat and fibre - the only convincing evidence of changes resulting from
selection applies to fibre, where selection of a "fibre line" in the Jiulong
breed appears to have produced far higher yields than in contemporary animals
not selected for this trait (Cai Li et al., 1980). Because fibre traits
are quite strongly inherited and much more so (at least in other species) than
milk yield or growth traits, selection progress is relatively easier to achieve
with fibre production traits.

The milk yield of yak is very low, relative to other cattle,
particularly those specializing in milk production. It has been suggested that
the amount of milk produced by yak is only the quantity that would normally be
needed to rear its calf. Thus, yak calves that receive only some of their dams'
milk, because the rest is taken for human consumption, grow significantly less
well (see Chapter 6). An incentive to select for a higher yield in yak is most
likely to arise only where there is an expanded market for milk destined for
sale.

In respect to meat output from yak, three problems arise that
may create conflict with opportunities for selection for growth rate or "size"
(meat production), even if these traits were somehow measured. One is the fact
that a significant proportion of each year's growth of the animals during the
warm season is lost over the period of nutrient deficiency in winter and early
spring. This makes it difficult to see what an appropriate selection strategy
should be. If the strategy were to be the increase in the size of the adult
animal, say at the end of a growing season, the selection process would be
delayed to late in life and hence would make slow progress. A second constraint
is that when milk is taken from yak for human consumption and the calf is left
short, the precise effect on each individual calf is difficult to estimate (even
though an average effect of rearing practice is known). And in any case, there
is variation in the quantity of milk produced by the dams. Selection among
calves for growth rate therefore would be less accurate than in a totally
uniform rearing system. A third problem is the opportunistic nature of the
disposal of surplus stock that frequently occurs. The lack of a regular
marketing strategy for well-grown animals, combined with the relatively
rudimentary nature of the current marketing system, particularly in the remote
areas, works against selection for "meat".

Nonetheless, in the regions where yak products are in great
demand in the marketplace, it seems that herdsmen have acquired both the
knowledge and skill to improve production traits - even though it may be done
unsystematically and perhaps unconsciously. This is a possible reason why some
breeds are held in higher esteem than others. But different breeds are rarely
compared with each other in the same place and at the same time. So it is
difficult to quantify the extent of any genetic differences in performance of
the breeds, as distinct from differences in their looks.

Selection objectives for the chief yak
breeds in China

In general, there are no clearly defined breeding objectives
and no developed breed structure among herdsmen. Chinese animal scientists,
however, decided towards the end of the 1980s to develop breeding objectives for
the principal yak breeds. The intention was to provide technical assistance for
a more systematic approach to yak breeding and to aim for earlier maturity, to
improve the animal's shape for meat production and to develop strains for either
milk or meat, or for meat and hair production. The criteria to be adopted
therefore stressed body size, growth rate, dressing and meat percentages, milk
yield and fat percentage, as well as the yield of hair - both coarse and down,
but with an emphasis on the down.

The criteria proposed were approved in Sichuan and Qinghai for
the Jiulong, Maiwa, Plateau and Huanhu breeds of yak (Zhong Guanghui et
al., 1995; Wen Yongli et al., 1995) and a corresponding scheme was
developed in Gansu for the Tianzhu White breed in 1985 (TAHVS and DAS, 1985).
Some information and comments about these schemes appear below, but first
though, attention is drawn to a selection procedure used by herdsmen. The
procedure in the Jiulong breed is regarded as traditional because it occurred
before the advent of the recent provincial schemes and also had particular
involvement from the late Professor Cai Li and his colleagues (1980; GAAHB and
YRO, 1980a, b).

A "traditional" selection procedure
used by herdsmen in the Jiulong area of Sichuan

Selection of yak by the herdsmen in the Jiulong area is
relatively systematic. Herdsmen pay more attention to choice of yak bulls for
breeding than they do to the cows. The guiding principle for the herdsmen is to
check the ancestors (the parents) first and the bull second. Selection of
replacement males starts in the herd with calves from cows that have good
conformation and high milk yield over two parities of calving. The herdsmen
require that the sire of the males being chosen as replacement bulls should have
copious hair and a large number of progeny. The bulls being selected should have
good conformation. In particular, the herdsmen require that the horns of the
selected bulls stretch outward from a rough base and that there is a long
distance between the horns. The forehead, head, muzzle and mouth have to be
broad; the neck thick and the lips thin and long; withers should be high and
brisket wide; the back, loin and rump should be wide and flat; the tail hairy;
forelimbs straight and hind legs curved; the scrotum should be shrunken.
Acceptable coat colours are black or black with some white specks on the
forehead and at the extremities of the body (e.g. legs or tail), but not on the
body itself.

It is of interest that selection of bulls in the Jiulong area
is made in three stages. The first is a pre-selection at the age of one to one
and a half years. There is a second selection from among the first group at the
age of three years and a final selection at the age of four to five and a half
years. (The relative importance given to different traits at each stage is not
specified). Bulls that are culled are castrated and used for meat or draught
purposes. After initial mating with cows, bulls that are found to have been
defeated in the normal competition for mates, which occurs among the bulls, and
males found to have physical defects or bad conformation are then also culled.
The herdsmen aim to have two or three successors to an excellent, dominant bull
that has been working in the cow herd.

In 1979, in accordance with newly instituted breeding plans,
nearly 7 000 reproductive bulls and cows (about a third of the total) were
evaluated on physical conformation and body weight (GAAHB and YRO, 1980b). As a
result, four adult yak bulls were identified that met or approached the
predetermined performance levels. However, by the time the bulls were identified
they were too old for use. Clearly, this was an uncertain start to selective
breeding and was more akin to a process of population screening (a search for
exceptional individuals) than a process of continuous genetic selection. This
particular scheme could not be continued, but consideration was subsequently
given to selection of yak at various locations and in different counties where
the Jiulong yak are kept (Cai Li, 1989). A standardized evaluation scheme for
the Jiulong yak was drafted and approved to assist individual evaluation and
selection (Zhong Guanghui et al., 1995). Finally, a nucleus herd with 412
breeding animals was established in the centre of the Jiulong yak territory and
106 individuals were maintained on a state farm to implement a breed-improvement
programme (Lin Xiaowei and Zhong Guanghui, 1998).

The traditional selection methods for Jiulong yak appear to
have produced over a period of many decades, perhaps centuries, an improved
breed of yak that is highly regarded. Clearly, the criteria applied contain
elements that are related to important aspects of production in the yak.
However, a cautionary comment should be added, lest it be thought that these
methods have to be unreservedly commended because they have tradition and
herdsmen's experience on their side. Geneticists would wish to suggest that
there is great scope for improving these procedures, even in the absence of
sophisticated indices of breeding value and modern computational procedures. To
start with, they would ask how closely related the physical appearance of the
yak, so much emphasized by the herdsmen, is to actual performance of the herd -
in terms of, say, growth, milk yield or reproductive rate. Usually the
relationship is not high. A geneticist would also wish to encourage the herdsmen
to pay most attention to those characteristics of the yak that provide the
greatest economic return irrespective of whether the products from the yak are
for home or commercial use. For that reason, it would also be urged that the
number of criteria considered for selection be restricted to an essential
minimum. Improvement of the important traits is diluted, or even lost, when a
lot of attention is paid to less important, even trivial, matters - as may be
the case now.

More recent provincial schemes: the
example of the Tianzhu White

The Provincial Administration of Standardization in Gansu
adopted criteria in 1985 to standardize the assessment of grading for the
Tianzhu White yak and to evaluate breeding value as an aid to selection (TAHVS
and DAS, 1985; Zhang Rongchang, 1989). The aim was to improve the breed for meat
and hair.

Scores are allocated for aspects of general conformation, the
body, testes for males and udder for females, legs, feet and the coat. Calves
and adults are graded to somewhat different criteria. Weight and height classes
are designedaccording to age and sex of animal and assigned to four
grade classes. The use of selected breeding bulls is recommended, and newborn
animals may be assigned a grade on the basis of the grades of their parents.
Breeding bulls, in turn, are classified into four grades on the basis of the
grades attained by their offspring. There are eight nucleus herds with a total
of about 400 breeding animals maintained in the central area of this breed and
40 multiplier herds with approximately 20 000 individuals in surrounding areas
(Zhang Haimin and Liang Yulin, 1998).

On the face of it, this scheme, like the "traditional" Jiulong
scheme, pays considerable attention to aspects of the animals' appearance. This
may well detract herders from considering more single-mindedly the performance
aspects that matter most, namely, in line with the objectives for this breed,
meat and hair production and the underlying factors of reproduction and vigour.
Also, as has been found elsewhere with breeding schemes, if too many traits are
considered there is a likelihood that none are improved (unless combined in
highly sophisticated, statistically complex and computerized schemes).

In spite of reservations about the selection schemes, there
appears to have been significant progress in the Tianzhu White yak since the
1980s. For example, the body height of adult breeding bulls and cows older than
four and a half years increased from 108.1 cm and 104.3 cm (average of 17 males
and 88 females) in 1981 to 110.2 cm and 104.7 cm (20 males and 44 females) in
1987 and to 114 cm and 112.9 cm (98 males and 826 females) in 1997.
Corresponding body weights changed for males and females from 189.7 kg and 171.4
kg to 199.2 kg and 179.6 kg and to 202.8 kg and 192.7 kg respectively over those
same years (Zhang Rongchang, 1989; Wang Yuchang and Wang Yanhong 1994; Zhang
Haimin and Liang Yulin, 1998). However, these data were collected in a simple
survey on various farms over a period of years. It is not possible, therefore,
to distinguish any contributions from genetic improvement from those in
management and feeding (or simply from year effects). There is a presumption,
though, that management and feeding practices have remained largely unchanged
over this period.

Other schemes

Sarbagishev et al. (1989) referred to an organized
breeding programme in Kyrgyzstan based on specifications for yak males and
females that were concerned primarily with conformation, growth rate and body
size. Pedigrees were included and breeding values constructed. The improvement
scheme was spread over a number of stock-breeding farms.

But the main scientific effort towards genetic improvement of
productivity of yak, in many countries, has been directed at hybridization with
Bos taurus and, to a lesser extent, Bos indicus cattle, rather
than to selection. Some consideration has also been given to introducing, by
crossbreeding, genes from wild yak into the domestic yak population as a means
of improving productivity (see the following section). Lei et al. (1994)
reported a scheme that uses performance criteria of individual yak and the
potential benefits of introducing wild yak.

In the late 1980s, the first Wild Yak Frozen Semen Station was
established on the Datong Yak Farm in Qinghai with three wild yak bulls (two
captured from the Qilian mountains and one from the Kunlun mountains (Lu
Zhonglin and Li Kongliang, 1994; Bo Jialin et al., 1998). Another Yak
Frozen Semen Station is now in operation at Damxung in Tibet (Zhang Yun, 1994).
These are the only A.I. centres in China specific to yak. By 1995, 8 700
crossbred animals of the wild yak with domestic yak had been produced in Qinghai
and Gansu that served as the base herds for further selection and breeding of
the new improved yak strain of Datong yak (Bo Jialin et al., 1998). The
scheme used in this development of a "new" breed is described in Chapter
2.

Zhang Yun (1994) reported that there were ten yak bulls from
the Sibu and Jiali yak breeds in Tibet and 28 semi-wild yak (F1, or backcrosses)
at the Damxung station, though this number had been reduced to 17 in use. At the
time of Zhang's report, 50 000 doses of semen had been produced and 2 000 yak
cows inseminated - as well as a much larger number of yellow cattle to produce
hybrids with the yak.

As yet there is no information on progeny records from these
A.I. bulls. The full potential of using such information in selection procedures
for improved performance of yak has not yet been realized. However, Zhang also
suggested that the distribution of yak semen from this station could play a
significant role in counteracting adverse effects of inbreeding, which have been
thought to occur in yak in some areas. (The need to introduce yak "blood" from
outside sources, to counteract inbreeding in the yak population of different
areas, is also referred to by Pal in relation to India [see Chapter 11, part
2].)

Group breeding schemes

Because of the potential advantages of group-breeding schemes
in promoting genetic improvement, especially when the participating herds are
each relatively small, consideration is being given to setting up such schemes
for yak. At present, as far as is known, these remain in the planning
stages.

In the early 1990s an "open-nucleus" herd was established at
Longri farm in Hongyuan county. This set-up included a small trial to check
problems in the recording of accurate pedigrees for purposes of estimating
genetic parameters (Zhong Guanghui, 1998). The nucleus herd to promote the
improvement of Maiwa yak consists of 12 breeding bulls, tested for their
performance, and 180 breeding cows (Lin Xiaowei and Zhong Guanghui, 1998).
Records of growth, milk and reproduction have been collected
continuously.

Consideration of inbreeding in
yak

Inbreeding has harmful effects on nearly all aspects of
livestock performance. Inbreeding reduces, for example, reproductive capacity,
growth rate, adult size, and milk production and increases mortality, especially
among the newborn and young. The amount of harm is usually quite closely related
to the degree to which inbreeding occurs. It is a matter that should be
considered in relation to yak because the traditional pattern of breeding may
encourage inbreeding (cf. Chapter 5). In this system, bulls compete for mates
and, in due course, these bulls are often replaced in the hierarchy of the herd
by their offspring. This makes it inevitable that some inbreeding occurs.
Inbreeding can be much reduced if bulls are exchanged across herds and greater
distances - even then the problem may not be avoided but only postponed if two
villages, for example, were consistently to exchange breeding stock only with
each other. Controlled mating, whereby the herdsman decides on the mates for a
particular bull, is similar in that it may reduce or postpone inbreeding, but
rarely avoids it for long.

The absence of the pedigrees of animals in yak herds has made
it impossible in the past to know the actual extent to which inbreeding has
occurred. However, recently, microsatellite markers were used to analyse the
genetic structure of different yak breeds/herds in China and other parts of the
world and hence to estimate a general inbreeding effect. An assumption is made
that the fewer alleles found at any one locus in a breed or herd, the higher
will be the degree of inbreeding in that population. These investigations may
help clarify the inbreeding issue specific to yak herds or breeds (cf.
Chapter 15). However, the actual effects in yak are not known since this
requires comparison of the performance of groups differing in their degree of
inbreeding. This, in turn, requires performance records linked to pedigrees. For
the time being, the probability of harmful consequences of inbreeding in yak is
therefore inferred from known, corresponding effects in cattle, sheep and other
livestock.

In some countries, such as Bhutan, Nepal and India (see
Chapter 11, part 2), concerns about the effects of inbreeding have been
expressed by those on the spot. The yak populations in these countries have
become relatively closed. This is a consequence of reduced interchange of
breeding stock across national boundaries relative to former times that, in
turn, increases the likelihood that related animals are mated to each other. The
effects of inbreeding must be suspected whenever the general performance of the
stock is known, or thought, to have declined relative to an earlier era, and
when other systematic changes in husbandry practices, such as overgrazing, for
example, cannot account for it. Thus Kozlovskii (1960) stated that yak in the
Gorno-Altai region were becoming closely inbred, which, if true, could well
account for the earlier view of Denisov (1935) that the yak of that area were
inferior, at that time, to those of other regions. Kozlovskii advocated, by way
of remedy, the introduction of unrelated yak males and/or of hybridization with
other cattle.

Inbreeding occurs whenever animals that are more closely
related to each other than "average" are mated to each other. For example, if a
son or sons of a popular bull are used in a herd as his replacement, they, in
turn, are liable to mate with some of their half-sisters or cousins. Moreover,
such bulls are likely to serve other less closely related females, but related
through common ancestors more generations back (grandparents or
great-grandparents). Mating of full siblings to each other, or parents to their
offspring, which is regarded as close inbreeding, can easily occur if steps are
not taken to avoid it. Pal et al. (1994), writing in relation to yak in
India, stated that farmers may use the same male to serve females of two to
three successive generations.

Inbreeding also occurs as a consequence of selection, even
though selection is widely and correctly advocated and practised for the genetic
improvement of livestock. Selection has the inevitable consequence of bringing
about an increase in inbreeding, simply as a consequence of restricting the
number of animals that become parents of the next generation. The objective in
selection schemes must ensure that the beneficial effects of selecting superior
stock outweigh the harmful effects of the consequent inbreeding. This
consideration is nowadays a routine part of large-scale and long-term breeding
plans, such as cattle improvement programmes involving the widespread use of a
few bulls through artificial insemination.

The reason for having dealt with the topic of inbreeding at
some length is that experience suggests that the effects of inbreeding are
easily ignored because they are not readily recognized in the short term.
However, the circumstantial evidence for inbreeding is strong in some yak
populations, and the potential for inbreeding should not, therefore, be ignored
when yak are allowed to mate.

Crossbreeding within the yak
species

No systematic crossbreeding appears to be practised among the
different breeds or local populations of yak. This is not surprising considering
the relative isolation of different communities and the distances separating
them. But it is more surprising that it does not seem, so far, to have played
more than a minor role in investigations to find out whether hybrid vigour would
result from such crossbreeding. There is a likelihood that hybrid vigour would
result, although the magnitude cannot be predicted. The likelihood of heterosis
from breed crossing can be argued from the relative isolation, over a long time,
of discrete populations of domestic yak in different localities and from the
likelihood that breeding practices within herds have led to inbreeding
(although, again, some would dispute this). Crossing under these circumstances
could have merits. From past experiments in China where Jiulong yak and Tianzhu
White yak were introduced to other localities for crossing with the local yak,
the crosses were at least heavier and larger than the local yak (Ren Chen
Luoerri et al., 1995; Liang Hongyun et al., 1997). However, in the
absence of results from the pure-bred animals of the introduced breed in the
same locality, it is difficult to know to what extent this improvement
represents the effects of heterosis or the consequence of bringing in "superior"
genes from the new breed. Table 3.1 gives some of these results for crosses with
the Jiulong yak.

Table 3.1 Improvement of the yak in Luhuo county in
Sichuan by crossing with the Jiulong yak [Source: Zhong Jincheng,
1996]

Type

Age (year)

Sex

No.

Average body weight (kg)

Average body measurements (cm)

Height

Length

Heart girth

F1 (Jiulong crossed with local)

Birth

M

10

13.8

54.4

48.1

57.6

F

12

13.2

54.4

49.2

56.8

0.5

M

8

46.9

71.0

77.4

89.7

F

10

41.5

68.4

73.6

86.2

1.0

M

8

85.0

95.7

107.7

127.3

F

8

80.2

90.3

103.3

122.7

Local Luhuo yak

Birth

M

6

11.9

53.5

46.3

56.2

F

6

11.0

51.6

46.0

54.0

0.5

M

6

36.6

66.3

69.3

82.0

F

4

29.9

63.3

67.8

81.3

1.0

M

3

81.3

85.0

93.3

109.3

F

3

77.8

80.3

90.7

106.0

Further support for the potential usefulness of crossbreeding
comes from the attention paid more recently to crossing of domestic yak with
wild yak and the claims of improved performance from such
crossbreeding.

In the results presented from such trials, it is also not
possible to differentiate clearly between the additive genetic effects (e.g. the
fact that wild yak are larger than domestic yak) and the occurrence and
magnitude of heterosis as a result of the crossing; but some results from such
crosses are shown in Table 3.4.

Size of pure wild yak

Measurements were made in the 1960s on five adult male wild
yak by the Agriculture and Animal Husbandry Department of Tibetan government
(Study Group [Qiangtang], 1978). These animals had been caught in the Qiangtang
area of northern Tibet. Their measurements are shown in Table 3.2.

Table 3.2 Body dimensions and weight of five male
wild yak from Tibet

Body dimensions (cm), weight (kg)

Average

Range

Head length

61.1

(55 - 67)

Forehead width

27.3

(26 - 32)

Circumference of base of horn

(30 - 40)

Body length

179.3

(171 - 193)

Height at withers

158.8

(152 - 163)

Heart girth

240.6

(218 - 264)

Chest depth

91.1

(90 - 92)

Chest width

61.6

(53 - 78)

Cannon bone circumference

(22 - 24)

Estimated body weight

1 000.0

Some wild yak calves caught by staff of the Animal Husbandry
Institute of the Yushu Tibetan autonomous prefecture of Qinghai province were
compared with domestic yak calves under the same conditions of feeding and
management (Xu Guilin, 1985). Table 3.3 shows the weights and weight gains of
the two groups. It can be seen from these results that the wild yak calves were
86 percent heavier than the domestic yak calves at three months of age but,
relative to their weight, grew more slowly (though not necessarily less in
absolute terms) so that by the age of 16 months the wild yak were only 63
percent heavier than the domestic ones.

Table 3.3 A comparison of the body weights and weight
gains at various ages of five wild yak and 19 domestic yak kept under the same
conditions of feeding and management [Source: Xu Guilin, 1985]

Age (months)

3

4

5

6

12

16

Domestic yak

Weight

33.6

39.2

48.2

51.5

59.1

67.4

gain (kg)

5.6

9.0

3.3

7.6

8.3

Wild yak

Weight

62.5

71.9

77.3

81.5

92.5

110.1

gain (kg)

9.4

5.4

4.2

11.0

17.6

Crossbreeding of wild yak with
domestic yak

Some results from the crossing of wild yak with domestic yak
are available. Provided the progeny from such crosses of domestic with wild yak
have not been given preferential treatment over the domestic yak alongside them
(and that may be a matter in question), the results suggest that the crosses
have an advantage. Lu Hongji et al. (1987), for example, showed that the
birth weight of crosses between domestic and wild yak were more than 30 percent
heavier at birth than domestic yak calves. By age six months, the advantage in
favour of the cross had increased to more than 50 percent. Calves with only one
quarter wild-yak blood were 16 percent and 35 percent heavier at birth and six
months of age, respectively.

Staff at the Lanzhou Institute of Animal Husbandry and
Veterinary Science of the Chinese Academy of Sciences used some frozen wild yak
semen to inseminate female domestic yak on the Datong Yak Farm of Qinghai
province (Lu Hongji et al., 1987). They also produced some backcrosses of
the F1 to local domestic yak (to produce 0.25 percent wild yak) and mated some
local domestic yak to males of the Jiulong (domestic) breed of yak (cf. Chapter
2, Datong breed). The results are shown in Table 3.4 and suggest that crossing
to the wild yak increased body weights and weight gains over the first six
months of life. These weight gains were greater, relative to the birth weights,
in the crosses with wild yak than in crosses with the Jiulong. The local
domestic yak showed the lowest relative weight gains to six months old. There
were no measurements beyond that age. Some of the wild-domestic crossbred yak at
the Datong farm are illustrated in Figure 3.1.

In the 1990s, there was intensive use in Qinghai of the wild
yak semen by A.I., or the use of semi-wild yak bulls with natural mating, to try
to improve the domestic yak productivity and "rejuvenate" the yak population.
Some comparable data from observations of the F1 (half wild yak blood), B1 (one
quarter wild yak blood) and local yak under the same feeding and management
system in southern Qinghai are shown in Table 3.5 (Yan Shoudong, 1998). It was
found that the body measurements and weights of the semi- (F1) and quarter-wild
yak (B1) were higher than those of domestic yak within the same age groups. As
seen from Table 3.5, birth weight, height, length and heart girth of the F1 were
greater than of the domestic yak calves and particularly at 18 months old, the
measurements of both the F1 and the B1 were greater than of domestic
yak.

Interest in the use of the wild yak to improve production of
domestic yak was exemplified by the presentation of a number of papers on this
topic at the first, second and third international congresses on yak, held in
China in 1994, 1997 and 2000 (Zhang Rongchang et al., 1994; Yang Rongzhen
et al., 1997a; Han Jianlin et al., 2002; Zhao Bingyao and Zhang
Jianwen, 1994). It was noted in those papers that, historically, herdsmen in the
Gannan area of Gansu drove their domestic yak females into regions where wild
yak lived, in order to allow natural mating with wild yak bulls. The crossbred
progeny would later be selected to improve the domestic yak population. Based on
this popular experience, more systematic studies using frozen semen from wild
yak bulls are in progress. Substantial numbers of first-cross and backcross (25
percent wild yak) offspring have been born and are reported to grow
significantly larger than the local domestic yak. The benefits of wild yak
blood, as noted in these studies, have also carried over into crossing with the
local yellow cattle. When yak bulls that had 50 percent wild yak blood were
mated to yellow cattle, the resulting F1 hybrids were of the order of 20 percent
larger at six months old than comparable F1 hybrids of yellow cattle with
domestic yak. Yang et al. (1997b), Lu and Zhao (1997), Yan Shoudong
(2002) and Amarsanaa et al. (2002) presented similar findings using wild
yak to increase the growth and the related meat production of the domestic
yak.

It is not known, from any of the studies previously referred
to, what is the relative importance of the role of heterosis and of the additive
genetic contribution from the wild yak to its cross with the domestic yak, as
discussed earlier in relation to crosses among domestic breeds of yak.

Results of studies in another area of Gansu (Lu Zhonglin and
Li Kongliang, 1994) suggested that substantial increases in body size, hair
production and meat output were achieved in first crosses of wild with domestic
yak, relative to the latter. Milk yield was found to have increased by more than
10 percent. Yan Ping et al. (1994) reported, more specifically, that the
fleece weight of adult females was 1.76 kg, 1.65 kg and 1.47 kg for half-wild,
quarter-wild and domestic yak, respectively. These authors also found that,
importantly, the proportion of the undercoat was increased substantially with
the introduction of wild yak blood - but the strength of the fibres was not
affected. The use of wild yak to improve domestic yak performance through a
process of crossing and selection was also reported to be under investigation in
Qinghai (Lei Huanzhang et al., 1994).

But clearly, only the additive genetic contribution from the
wild yak genes will be useful in the actual process of subsequent selection
(though the cross will retain some of the advantages from the initial
heterosis). It is the perceived advantages of the introduction of wild yak blood
into domestic yak populations that led to a project to develop a new breed from
such a crossbred foundation (see Chapter 2).

Breed conservation

Taking into account the size of the present domestic yak
population as a whole, it would be difficult to argue that conservation measures
are a matter of urgency at this time. This might change if social or economic
pressures were to reduce the extent of yak keeping - as is already evident in
some areas, such as Nepal - or if predicted changes in global climate (over
decades and centuries) have the effect of restricting the future distribution
and size of the yak population.

Preservation of some of the remarkable traits of the yak in
terms of its adaptation to a harsh environment and to long periods of severe
deprivation should, nonetheless, be of interest to animal breeders worldwide.
There are parts of the world where these characteristics could assist in
establishing animal production and other parts where such resilience, on the
part of the animal, could lead to better utilization of natural resources.
Currently, however, the gene pool of the domestic yak as a whole is not
endangered.

A different situation seems to exist for some of the more
localized, and to an extent differentiated, populations or breeds of yak. The
total numbers in some of these breeds is not large and hybridization with Bos
taurus and Bos indicus cattle further reduces the proportion of the
yak population available for its replacement.

For example, the Jiulong yak, possibly the best producer among
the yak breeds, numbers 50 000 animals (Zhong Jincheng, 1996; Lin Xiaowei and
Zhong Guanghui, 1998). The total numbers, however, tell only a small part of the
story. Starting from a small herd, the Jiulong breed of yak has been a closed
population for hundreds of years. Throughout the breed's history, herdsmen are
said to have avoided introducing outside blood. Moreover, the system of
selection practised by the herdsmen (previously described), and the natural
competition among bulls for dominance makes it virtually certain that the
effective size of the population is small and that inbreeding occurs (though the
extent of this is a matter for debate). Thus, if the particular properties of
the Jiulong are worth preserving and are not to be lost through genetic drift,
special measures may be required. This was recognized by Chinese experts some
years ago and led to the setting up of a random-breeding herd of 100 yak females
and 20 males maintained per generation (Zhong Jincheng, 1996).

This was managed in the Hongba area of Jiulong county and was
the responsibility of the Animal Husbandry Station there. Income from the sale
of milk and culled animals met some of the costs. There was also a subsidy from
local government to assist the project. This type of approach is clearly
commendable as one way forward in terms of breed conservation. A random-breeding
herd has, however, a further potential advantage in that it can also serve as a
yardstick against which to measure progress from any genetic selection in other
parts of the breed population.

Other yak breeds may be in a similar situation to the Jiulong,
with total numbers not large and the size of the "effective" breeding population
possibly quite small. The Tianzhu White breed, in an area of Gansu province,
could be one and its conservation is being considered (Wang Yuchang and Wang
Yanhong, 1994). Zhang Haimin and Liang Yulin (1998) indicated that the number
and proportion of the pure white yak in Tianzhu have increased as a result of
the protection programs; for example, in 1952, the proportion of pure white
animals was 20.3 percent and in 1981 it was 31.5 percent. It increased to 44
percent in 1998. Interestingly, the price of a white tail was double that of a
black one in 1998 (120 yuan per kg compared to 60 yuan per kg).

Local breeds may have special merits or special
characteristics that could be lost in the absence of positive action to maintain
such breeds. Investigation of the need for conservation in the yak should
therefore receive some attention even if local rather than general action may be
called for. A useful start might be an up-to-date census of the yak population,
its various types and breeds and current breeding practices. In combination,
such information would help to indicate the (genetically) effective size of the
different breeding populations, both in China and elsewhere. A census of numbers
alone, as regularly practised in some countries such as Mongolia, though
helpful, is not enough for this particular purpose.

Too often in matters of conservation, action has been delayed
until damage to the breed, or even extinction of the species, has become
imminent. This must not be allowed to happen with the yak.

The genetic approaches using chromosomal and protein
polymorphisms, mitochondrial DNA RFLP and sequencing, and microsatellite
genotyping (referred to in Chapter 2) to estimate genetic distances among breeds
should go some way towards determining priorities for breed conservation (Han
Jianlin, 1996, 2000). (The technology is discussed in more detail in Chapter
15).

For the wild yak, it is widely accepted that conservation is a
matter of importance and urgency. Accounts, from as recently as the nineteenth
century, testified to vast herds of wild yak in the Kunlun mountains of Tibet
and Qinghai. These are no longer seen. Miller et al. (1994) estimated
that wild yak of all ages and both sexes may still have numbered around 15 000
in the early 1990s, and this is also the number quoted more recently by Schaller
(1998). Miller and Schaller (1996) claimed an estimated 7 000 - 7 500 wild yak
remained in the Chang Tang Wildlife Reserve in Tibet at the time of their
survey. But this number does not necessarily give an accurate picture of the
threat confronting this wild species. Wild yak in China are included in the
country's wildlife-protection legislation, but, according to Miller et
al. (1994), the Departments concerned have inadequate resources for
enforcement. The factors that have led to a dramatic decline in wild yak numbers
over the past century still operate, even if to a lesser extent. These factors
include excessive hunting, partly for food, the encroachment of the
infrastructure of modern society, such as roads, and the increasing competition
for grazing land from domestic livestock (Miller et al., 1994).

Hybridization of yak with cattle of
other species

Ancient documents show that yak have been hybridized with
ordinary cattle (Bos taurus) for at least 3 000 years. Documents from the
eleventh century China, in the Zhou dynasty, suggest that hybridization of yak
with cattle by the Qiang people gave benefits that nowadays would be called
heterosis (or hybrid vigour). The name Pian Niu and variants of it have
been used for these hybrids from earliest times (Ceng Wenqiong and Chen Yishi,
1980; Xie Chenxia, 1985; Cai Li, 1989). However, many other names exist (see
section on local names). In some areas, such as northern India, Nepal and
Bhutan, hybridizing with Bos indicus cattle also occurs.

Systematic hybridization of yak with other cattle has been
recommended and practised for many years - and certainly as long as
hybridization by plant breeders has been in fashion. The hybrids find a special
niche with herdsmen in providing extra milk and as draught animals, usually at
somewhat lower altitudes than the typical yak country. Hybridization is carried
out primarily with yak females mated to bulls of local cattle.

This is regarded as the normal hybridization and, in China the
F1 is called "true Pian Niu" (or simply Pian Niu). The reciprocal
hybridization of female cattle to yak bulls is also practised and regarded as
"counter-hybridization" with the progeny called "false Pian Niu" (see
Figure 3.2) and many other local names.

The hybrids are always mated back to either yak or cattle
males. There is no alternative to this as the F1 males are sterile. The herdsmen
use, for the most part, the cattle available to them in their area; in China,
for example, they are the local, so-called "yellow cattle". The hybrid progeny
of the F1 generation are then called "local Pian Niu". However, much
investigation has gone into the use of "improved" breeds of cattle of dairy,
beef and dual-purpose types. Results of hybridizing with both local and
"improved" cattle breeds are given in Chapter 7. The name that is given to the
first hybridizing of yak with "improved" cattle breeds is "improved Pian
Niu" - in order to distinguish it from the "local Pian
Niu".

Information on the production of hybrids between yak and
cattle will also be found in Chapter 11 in relation to individual
countries.

In the course of experiments in the 1920s and 1930s at Buffalo
Park, Wainwright, Canada, aimed at developing a meat animal for the cold
northern regions, including Alaska, a small number of hybrids were also
successfully produced between yak (male) and female American bison and
half-bison (bison crossed with a cattle cross) (Deakin et al.,
1935).

Local names for hybrids

Names for the first generation hybrids of yak and cattle
include the name dzo in Tibetan areas, variants of which extend into
Mongolia and other countries, and chauri, the name used in Nepal. The
various types of backcross hybrid, both to cattle and to yak, have an especially
rich variety of names that differ in different parts of China and elsewhere.
Descriptions of these names have been given by, among others, Zhao Zhengrong
(1957), Hu Angang et al. (1960), Cai Li (1980), Joshi (1982), Zhang
Rongchang (1989) and Pal (1993). The uninitiated traveller may find himself
confused by the fact that the local people in China are said to call the hybrids
of yak with cattle "improved cattle" - this usage is avoided here.

Distribution of hybrids

In the areas of the Henduan Alpine type of pasture,
hybridizing of yak females with cattle males is not widely practised, nor is
interspecies hybridization common in the pastoral regions at high elevation to
which cattle cannot adapt. Such hybridization is, however, widespread in areas
of mixed pastoral and agricultural production at lower altitudes. Table 3.6
shows, by way of example, the relative proportions of pure yak to hybrids and
yellow cattle in two such areas in Sichuan. In the main yak-producing areas,
hybridization with cattle is normally restricted to only a small proportion of
the yak herd (see section, Limits to hybridization).

Nomenclature

Because of the diversity of local names for different stages
of hybridizing and in order to avoid confusion in the presentation of results in
this and later chapters, the scientifically more formal nomenclature of F1
(first-generation hybrids), and B1 (backcrosses), etc. will be used. It should
be noted that in publications from China and some other countries, the
backcross-hybrid generations are often denoted as F2, F3, F4, etc. This
nomenclature will not be used here as it also could lead to confusion among
readers, geneticists in particular, who will be accustomed to these notations
denoting successive generations of crosses (or hybrids) mated among themselves.
Backcross hybrids will be described here by the letter B, with a number denoting
the generation and a letter to show whether the last male used was cattle or yak
- when that has been specified. (Thus, B1(C) would denote a backcross-hybrid
animal produced from the mating of a F1 female to a cattle bull, etc.). In the
same way, in cases where doubt could arise, the F1 generation will indicate
whether the sire was a cattle breed or a yak.

Table 3.6 Proportions of yak, Bos taurus
cattle and hybrids in Ganzi county of Sichuan

Type

Pastoral area (%)

Agricultural area (%)

Yak

91.4

16.8

F1

7.8

55.8

B1(C)

0.7

3.7

Cattle

<0.1

21.9

Total No.

41 541

25 560

The hybrid females are an important source of milk and milk
products, for home consumption or for sale, and the males, since they cannot be
used for breeding, are used for draught purposes, or are slaughtered for meat
(see Chapter 7).

In China, the reciprocal hybridization procedure between yak
bulls and yellow cattle females is carried out mainly in the cattle-producing
areas of the cold Minshan mountains, especially in the Min county of Gansu
province and Pingwu county in Sichuan province. These hybrids do not give much
milk and are used mainly for draught purposes.

Hybridization policy

The first generation of hybrids of yak and "ordinary" cattle
adapt well to the conditions in which they are used. They have some of the good
characteristics of both parental types: resistance to a harsh environment from
the yak and extra productivity, milk in particular (but with a lower fat
percentage), from the cattle. Backcross hybrids to cattle, however, are less
well adapted to the environment, and their productivity is often little better
than that of yak - most probably through loss of heterosis (although there is no
strict quantification of this). Backcross hybrids to cattle are not therefore
favoured - one practice being to dispose of these hybrid calves immediately
after birth, in order to have all the milk from the dam available for use or
sale by the herders.

The alternative of backcrossing to the yak does, however,
provide a particularly good source of animals for meat production. This system
is encouraged and practised in China and elsewhere.

Cai Li et al. (YRO and XLF, 1983; YRO and GISP, 1984)
showed, from a comparison of two neighbouring and otherwise similar grassland
farms in Sichuan, that the output per head of animal, per unit of land and per
unit of labour can be seriously reduced if the proportion of B1 hybrids is
allowed to become too high. On the Xiangdong Livestock Farm, the proportion of
B1 hybrids was not allowed to exceed 5 percent of the total herd and some
selection was practised of those retained. On the other farm, Axi Livestock
farm, the backcross progeny of the F1 hybrid generation were retained in full.
The results of the comparison are shown in Table 3.7.

The use of "improved"
breeds.

In China, starting at Datong in Qinghai province around 1939
and in the area now known as the Ganzi Tibetan autonomous prefecture in Sichuan
from 1941, some yak were crossed with Dutch Holstein-Friesian bulls. Such
hybridization did not become systematic until the mid-1950s when 200 bulls of
various breeds were introduced to the yak-producing areas of China (Zhang
Rongchang, 1989). The breeds included the Holstein-Friesian, Shorthorn,
Simmental; Latvia, Ala-Tau, Kostrome cattle, the Mongolian, Binzhou, Sanhe,
Qinchuan, Yinging and others. More recently, Charolais, Hereford, Limousine and
others have been added to those available for hybridizing with yak. Mating was
tried initially by natural mating, but artificial insemination was also used and
continues as the predominant practice (Cai Li, 1989; Zhang Rongchang, 1989).
From 1979 to 1985, a yak research team coordinated the hybridizing with such
exotic breeds in the five principal provinces with yak in China, and some 32 000
hybrids were produced. As so often happens with fieldwork, relatively little of
this work has provided comparative performance results - those available are
quoted in Chapter 7.

Table 3.7 Comparison of output of animal products
from two neighbouring and similar farms in pastoral areas of Sichuan province
(1977 - 1981)

To better exploit the advantages of hybridization while
avoiding the reproductive problems caused by using large "exotic" bulls, an
alternative has been devised in parts of China whereby crossbred cattle, instead
of large exotic breeds, are hybridized with the yak. For example, the Holstein
Friesian or Simmental breed was used to produce F1 breeding bulls by crossing
them first, by A.I., with the local cattle. The F1 crossbred bulls, with their
relatively smaller body size, were then used on the yak to produce a hybrid F1
through natural mating.

Although the growth and performance of the hybrids for both
milk and meat production was highly regarded (see Chapter 7, for performance
results) the bulls of these various "improved" breeds (and 75 percent grade
bulls of these breeds with yellow cattle) did not adapt to the local conditions
and high altitudes in China. Most of the bulls died of mountain sickness or for
other reasons within two years of introduction, and many died within the first
few months. The bulls introduced in the mid- and late 1950s left fewer than 1
000 F1 and B1 hybrid progeny over a more than 20-year period.

Hybridization of yak with these "improved" breeds of cattle is
now carried out by A.I. with frozen semen. This procedure inevitably restricts
the utilization of these breeds to the more accessible and well-organized yak
herds. In practice in many areas, therefore, the Bos taurus (and Bos
indicus) cattle used for hybridizing with the yak will continue to be the
local types of cattle.

Hybridization of yak with "exotic" breeds of cattle has also
been practised in other countries for a long time (see Chapter 11, part 2), such
as in as, some countries of the former USSR. Thus, Denisov (1938) reported on
hybrids of yak and Schwyz (Brown Swiss) cattle, and more recently Katzina et
al. (1994) added the Jersey and the Galloway and a continuing use of the
Schwyz (now of American origin, hence probably the American Brown Swiss) to the
list of exotic breeds referred to previously. Several of the breeds referred to
are also used in Mongolia (Zagdsuren, 1994).

Limits to hybridization

The relatively low reproductive rate of the yak sets severe
limits on the proportion of the female yak population that can be used for
hybridizing with cattle if the numbers of the pure yak population are to be
maintained, or possibly increased. In practice, it has been found best to
restrict production of hybrids to the F1 generation only (whose offspring, in
turn, are then slaughtered for meat). The male sterility of the hybrids prevents
inter-se crossing systems and allows only the mating of the F1 hybrid
back to yak or cattle bulls. Reduced productivity, relative to the F1, makes the
B1 and later backcross generations unattractive commercially.

The actual proportion of the female yak population that can be
hybridized with cattle depends on the reproductive rate, the replacement rate
for cows (depending on the rate of death and disposal of the cows) and the loss
of female calves before they reach reproductive age. These factors will vary
from region to region and from year to year.

If it were assumed that:

the yak population
remained static in numbers,

an average reproductive rate
for the yak cow is around of 0.5 (equivalent to a live calf every second
year),

10 percent of cows are
eliminated annually and

10 percent of calves are lost
before breeding age,

then 50 percent of the yak cow population could be available
for hybridization. (These assumptions are equivalent, on average, to a yak cow
producing, in her lifetime, two female progeny that survive to breeding age.)
Any intention to expand the yak population would reduce the proportion that
could be hybridized. If an increase of 10 percent in population numbers were
required (and, as indicated earlier, herdsmen like to increase the number of
animals they own), then only 10 percent of the yak cows could be hybridized with
cattle - when the other assumptions remain the same.

Other assumptions would be entirely reasonable. Thus, higher
replacement rates for cows and poorer survival of calves would reduce the
proportion of yak females available for hybridization. For example, if
replacement rates for cows and mortality among calves were both as high as 20
percent, as happens in some situations and some years, no yak cows would be
available for hybridization if the reproductive rate of the yak did not exceed
50 percent - even with a static yak population. Matters would be even worse if
snow disasters strike in particular years and localities and the rebuilding of
the pure yak population becomes the top priority. On the other hand, in some
regions and countries, where reproductive rate over a lifetime of the yak may be
higher than in the examples given, the proportion of the yak female population
available for hybridization can be increased.

The precise proportions of the yak population available for
hybridization thus depend on the circumstances in any particular herd or group
of herds. The point has been made often (see also Chapter 7) that the production
of yak-cattle hybrids can play a useful role in improving the economics of
animal production in the mountainous regions and particularly at the lower
elevations of the yak territory and in the proximity to markets where the extra
produce can be sold. But it also needs to be said that such hybridization is not
a panacea. The pure yak must, perforce, remain the major proportion of the total
bovine population in the mountainous regions. The attractions of hybridizing yak
with cattle should not be allowed to detract from the need to consider genetic
and husbandry improvements for the yak itself. In fact, improvements in the
productivity and reproductive rate of the yak would also in turn increase the
opportunities for hybridizing of yak with cattle, as already apparent in some
areas.

There is clearly an opportunity to produce additional hybrids
from the reverse process, that of mating cows of other local, domestic cattle
species to yak bulls or using the semen of yak for insemination - although it
appears that this hybrid (the "false Pian Niu") is traditionally used
mainly for ploughing (see Chapter 7). This process also depends on having
available a reproductive surplus in the cattle population.

Recently, Professor Jack Rutledge (personal communication,
2002) made a technology-based proposal for trials to produce hybrids from
"improved" (e.g. Holstein) cattle and yak by in vitro production of
embryos - using oocytes from slaughter cattle and yak semen. The resulting
embryos then need recipient dams for their further development to birth. This
proposal was conceived in the context of a situation (in a part of the Andes)
where such hybrids might become a suitable dairy animal in the absence of either
the yak or of a sufficiently productive cattle population or alternative milk
producer. Although these procedures may have little immediate relevance to
traditional yak-rearing areas, the idea is intriguing (see also Chapter
16)

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